A cross national study of the diagnosis of childhood hyperkinesis is underway between the U.S. (NIMH) and the U.K. (The Maudsley Hospital) to understand the basis for the widely discrepant rates of diagnosis between the two countries. In the U.S., hyperkinesis accounts for nearly 50% of child guidance clinic cases, while in the U.K. this diagnosis accounts for less than 3%. A case history exchange has been completed between the two centers, and a longitudinal follow-up study will utilize a research team's diagnosis using ICD 9 and DSM III to examine predictive validity of the two diagnostic schemes.